307 



to very coarse agglomerates. Some of the fragmental 

 rocks are waterworn, and at least one bed of tuff is fossili- 

 ferous. The fossils, which are chiefly Eocene gastropods, 

 give the only evidence of the age of the volcanics and 

 place them definitely in the upper Eocene. The same 

 fossil-bearing tuffs are found to the south on the Olympic 

 peninsula [14]. It is probable that the eruptions of 

 the Metchosin basalts were largely of a quiet nature from 

 numerous fissures, and actual vents are doubtless repre- 

 sented by diabase dykes. That the eruptions were in part 

 explosive is fully substantiated by the occurrence of agglo- 

 merates and tuffs, and it is possible that the irregular 

 masses of coarse agglomerate represent the pipes or necks of 

 old volcanic cones. The absence of terrestial sediments 

 in the volcanics and the presence of marine organisms 

 suggests that the volcanics were accumulated under 

 marine conditions, presumably in deep water removed 

 from any continental mass. But the occurrence of water- 

 worn fragments and of marine fossils indicates that enough 

 lava was erupted to form a platform which reached nearly 

 to the surface of the water, and on which were built the 

 cones that projected above sea level. 



The Metchosin volcanics have been deformed and more 

 or less altered. They have a general northwest- 

 southeast strike and are evidently involved in several 

 folds although the prevailing dip is about 30 degrees to 

 the northeast. They are extensively sheared and faulted, 

 and their northern contact is a profound thrust fault, 

 which extends for 40 miles (64 km.) across the southern 

 end of the island. Farther west they are also intruded by 

 gabbro masses. The deformation and intrusion must 

 have taken place at or near the close of Eocene times, for 

 farther west the deformed and intruded rocks are uncon- 

 formably overlain by Miocene sediments. Some of the 

 alteration of the Metchosin volcanics must have taken 

 place during the deformation, but much of it has taken 

 place under surface conditions developing zeolites and 

 similar secondary products. 



Superficial Deposits — The drift deposits of the region 

 are of varied character, having been deposited by various 

 agencies during the different stages of glacial occupation 

 and retreat [7 and 8]. The oldest of the superficial 

 deposits, the Admiralty till, is confined to a few localities 

 and occurs in the crevices and small irregular hollows of 

 35069— 3 B 



